The present invention relates to a modular printhead for a color printer. In further aspects the invention concerns methods of printing and loading using the printhead.
The invention relates to a modular printhead for a color printer, including a plurality of nozzles to cause deposition of ink drops during a firing cycle of the printer.
There is disclosed herein a modular printhead for a color printer, including a plurality of nozzles, each nozzle effecting deposition of an ink drop to form a dot on print media during a firing cycle of said printhead, wherein said nozzles are arranged in pods, with said nozzles of each pod connected to a respective common ink supply line, the nozzles of each pod being arranged in a number of distinct rows, and pods of each different color being arranged together into operating groups in which selected mutually exclusive sub-groups of nozzles are gated to enable the nozzle of each sub-group to be fired simultaneously at predetermined phases of said firing cycle, one pod of each different color being grouped together to form a chromapod in which the pods of different colors are arranged so that the dots printed by the nozzles of one color will be for different lines than those printed by the other colors at the same time, but each pod of the chromapod will print the same group of dots in turn, one or more chromapods being formed into a phasegroup in which groups of nozzles are fired simultaneously during a given firing phase, and one or more chromapods being organised into a single podgroup, one or more podgroups being organised into a single phasegroup, one or more phasegroups being organised into a single firegroup in which the same nozzles are fired simultaneously, one or more firegroups making up a segment, and said printhead having a number of segments side by side.
In one example there are two rows of nozzles in each pod and the nozzles of one row deposit the even dots along one line on the page, and the nozzles of the other row deposit the odd dots along the adjacent line on the page.
The amount of offset between the rows of nozzles is designed to match the flow of paper under the nozzles.
The nozzles of each pod may be fired in order, along a first row starting from a first side, and then along the other row in the same direction ending at the other side.
A single pod may consist of ten nozzles sharing a common ink reservoir. Five nozzles are in one row, and five are in another. Each nozzle may produce dots 22.54 xcexcm in diameter spaced on a 15.875 xcexcm grid.
One pod of each different color may be grouped together to form a chromapod in which the pods of different colors are arranged so that the dots printed by the nozzles of one color will be for different lines than those printed by the other colors at the same time, but that each pod of the chromapod will print the same group of dots in turn.
One pod of cyan, magenta, yellow and black, may be grouped into a chromapod. A chromapod represents different color components of the same horizontal set of ten dots on different lines. The exact distance between different color pods is a constant number of dot-widths, and must therefore be taken into account when printing: The printing algorithm must allow for a variable distance of dot-widths between colors.
One or more chromapods may be formed into phasegroup in which groups of nozzles in enabled podgroups are fired simultaneously during a given firing phase. One or more of the podgroups of a phasegroup are enabled at the same time, depending of the speed of printing required.
Five chromapods may be organised into a single podgroup. Since each chromapod may contain 40 nozzles, each podgroup may contain 200 nozzles: 50 cyan, 50 magenta, 50 yellow, and 50 black nozzles.
Two podgroups may be organised into a single phasegroup. The phasegroup is so named because groups of nozzles within a phasegroup are fired simultaneously during a given firing phase. The formation of a phasegroup from two podgroups allows both low-speed and high-speed printing via two PodgroupEnable lines.
Two phasegroups may be organised into a single firegroup, with four firegroups in each segment. Firegroups are so named because they all fire the same nozzles simultaneously. Two enable lines allow the firing of the Phasegroups"" nozzles independently as different firing phases.
A 4-inch printhead will typically be made up of eight segments side by side, and each segment will have four firegroups.
A wider printhead may be made by assembling two of the printheads together. So an 8-inch printhead consists of two 4-inch printheads for a total of 51,200 nozzles.
The nozzle hierarchy allow overlapping phases and multiple speeds while maintaining even power consumption. In addition, the nozzle groupings pods provide physical stability.
In terms of power consumption, the nozzle groupings enable a low-speed and a high-speed printing mode to allow speed/power consumption trade-offs to be made in different product configurations.
A single 4-inch printhead may contain a total of 25,600 nozzles. A Print Cycle involves the firing of up to all of these nozzles, dependent on the information to be printed. To fire them all at once would consume too much power and be problematic in terms of ink refill and nozzle interference. Further, the firing of a nozzle also causes acoustic perturbations for a limited time within the common ink reservoir of that nozzle""s pod. The perturbations can interfere with the firing of another nozzle within the same pod. Consequently, the firing of nozzles within a pod should be offset from each other as long as possible.
To address this, one nozzle per color may be fired from a chromapod and then a nozzle from the next chromapod within the podgroup may be fired.
Two firing modes may be defined: a low-speed printing mode and a high-speed printing mode:
During low-speed printing, only one Podgroup of each phasegroup is given firing pulse, so only one podgroup of the two fires nozzles. In the low-speed printing mode the chromapods within both podgroups must all fire before the first chromapod fires again.
In the low-speed printing mode, 128 nozzles may be fired simultaneously from each 4-inch printhead. The fired nozzles should be maximally distant, so 16 nozzles are fired from each of the eight segments. To fire all 25,600 nozzles, 200 different sets of 128 nozzles must be fired.
During high-speed printing, both Podgroups are set, so both podgroups fire nozzles. In the high-speed printing mode the chromapods within a single podgroups must all fire before the first chromapod fires again.
In the high-speed printing mode, 256 nozzles may be fired simultaneously from each 4-inch printhead. The fired nozzles should be maximally distant, so 32 nozzles are fired from each segment. To fire all 25,600 nozzles, 100 different sets of 256 nozzles must be fired.
Consequently a low-speed print takes twice as long as a high-speed print, since the high-speed print fires twice as many nozzles at once. The power consumption in the low-speed mode is half that of the high-speed mode. Note, however, that the energy consumed to print a page is the same in both cases.
The printhead produces several lines of feedback to adjust the timing of the firing pulses. One feedback signal informs the controller how hot the printhead is. This allows the controller to adjust timing of firing pulses, since temperature affects the viscosity of the ink. A second feedback signal informs the controller how much voltage is available to the actuator. This allows the controller to compensate for a flat battery or high voltage source by adjusting the pulse width. A third feedback signal informs the controller of the resistivity (Ohms per square) of the actuator heater. This allows the controller to adjust the pulse widths to maintain a constant energy irrespective of the heater resistivity. A fourth feedback signal informs the controller of the width of the critical part of the heater, which may vary up to xc2x15% due to lithographic and etching variations. This allows the controller to adjust the pulse width appropriately.
A Load Cycle involves the loading up of the printhead with the information to be printed during the subsequent Print Cycle. The firing control port of each nozzle may have an associated NozzleEnable bit that determines whether or not the nozzle will fire during a Print Cycle. The NozzleEnable bits are loaded during the load cycle via a set of shift registers. Once all the shift registers have been fully loaded, all of the bits are transferred in parallel to the appropriate NozzleEnable bits. Once the transfer has taken place, the Print Cycle can begin. The Print Cycle and the Load Cycle can occur simultaneously as long as the parallel load of all NozzleEnable bits occurs at the end of the Print Cycle.
The printing process must produce data in the correct sequence for the printhead. As an example, a first Clock pulse may transfer the CMYK bits for the next Print Cycle""s dot 0, 800, 1600, 2400, 3200, 4000, 4800, and 5600. The second Clock pulse may transfer the CMYK bits for the next Print Cycle""s dot 1, 801, 1601, 2401, 3201, 4001, 4801 and 5601. After 800 SRClock pulses, the Transfer pulse can be given.
Of course, within the 800 SRClock pulses, the shift registers must be loaded according to the correspondence with the final transfer to the NozzleEnable bits, and here a number of different wiring possibilities exist. One loading (and hence wiring) possibility is to load the bits in pod order, and within each pod the bits representing each nozzle from one side of the pod to the other (effectively loading the first nozzle from the first row through to the last row before moving on to the second nozzle in the first row). In a 2 row pod this means loading the nozzles in an apparant zig-zag fashion. Another possibility is to load the bits in pod order, and within each pod the bits representing each row, and within each row starting from the nozzle from one side of the pod to the other.
It is important to note that the odd and even CMYK outputs, although printed during the same Print Cycle, do not appear on the same physical output line. The physical separation of odd and even nozzles within the printhead, as well as separation between nozzles of different colors ensures that they will produce dots on different lines of the page. This relative difference must be accounted for when loading the data into the printhead. The actual difference in lines depends on the characteristics of the inkjet mechanism used in the printhead. The differences can be defined by variables representing the distance between nozzles of different colors, and the distance between nozzles of the same color.